The present invention relates to a toner for use in a recording method utilizing electrophotography, electrostatic recording, magnetic recording, etc. More specifically, the present invention relates to a toner for use in an image forming apparatus, such as a copying machine, a printer or a facsimile apparatus wherein a toner image once formed on an electrostatic latent image-bearing member is transferred onto a transfer(-receiving) material for image formation.
Hitherto, various electrophotographic processes have been known, e.g., as disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. Generally, an electrical latent image is formed on a photosensitive member using a photoconductor material, and the latent image is developed with a toner to form a toner image, which is then transferred as desired onto a transfer(-receiving) material, such as paper, and fixed, e.g., by heating, pressing, heating and pressing, or with solvent vapor, to obtain a final image. Residual toner remaining on the photosensitive member without being transferred is cleaned by various methods, and the above-mentioned steps are repeated for a subsequent image forming cycle.
In recent years, such an image forming apparatus is frequently used not only as an office copying machine for simply reproducing ordinary originals but also as a printer as an output means for computers and also as a personal copier.
Accordingly, an image forming apparatus is required to further pursue a smaller size, a lighter weight, a higher speed and a lower power consumption, and correspondingly, the apparatus is becoming to be composed of simpler elements in various respects.
On the other hand, as methods for developing electrostatic latent images, there have been generally known the two-component developing method of using a developer comprising a toner and a carrier in mixture, and the magnetic mono-component developing method using only a magnetic toner.
The two-component developing method is rather contradictory to the requirements of smaller size and lighter weight in view of the use of the carrier and the necessity of a so-called ATR (automatic toner replenishing) mechanism for adjusting a ratio between the toner and the carrier.
The magnetic mono-component method is accompanied with a difficulty in providing a color toner.
In contrast thereto, a non-magnetic mono-component developing method as disclosed in Japanese Laid-Open Patent Application (JP-A) 58-116559, JP-A 60-120368 and JP-A 63-271371 is noted as a developing method for solving the above-mentioned problems. In the nonmagnetic mono-component developing method, a toner is applied onto a toner-carrying member by a layer thickness regulation means, such as a blade. The toner is triboelectrically charged through friction with the blade and the toner-carrying member surface, and the toner has to be applied as a thin coating layer since a larger coating thickness is liable to result in an insufficiently charged toner fraction, which causes fog or scattering. Accordingly, the blade has to be pressed against the toner-carrying member under a sufficient pressure, and the force applied to the toner at this time is larger than the one applied to the toner in the two component developing method or in the magnetic mono-component developing method. As a result, the toner is liable to be degraded, thus causing image defects such as fog and density lowering.
As a trouble accompanying the toner deterioration, toner blot-down is known, that is spotty image defects on images caused by toner agglomeration within a developing device during continuous image formation on a large number of sheets. As the image forming process speed becomes higher, the toner deterioration is liable to be promoted so that the above trouble becomes more noticeable.
As for image forming apparatus according to electrophotography, substantial development is being achieved so as to be adapted for higher functionality or multi-functional use or color image formation. On the other hand, the toner is becoming used in various severe environments in increasing cases, and accordingly, some problems are caused as follows in such severe environments.
One such problem is caused by wide spreading of electrophotographic image forming machines, inclusive of copying machines, printers and facsimile apparatus, over many countries in the world, and there have been increasing demands for achievement of high-quality images in the respective environments and similarly high-quality images on various grades of recording materials used in the respective companies.
Another problem is caused by toner melt-sticking onto the (latent) image-bearing member liable to be caused in a low temperature/low humidity environment, resulting in spotty image defects (lacks) on the images.
Another problem is roughening of halftone images in a low humidity environment, which is a phenomenon of resulting in images with a rough appearance causing an image quality lowering in a halftone image, such as a photographic image, that is liable to be caused by a lowering in developing performance of the toner.
Another problem is toner blot-down caused when the toner is exposed to high temperature. The toner blot-down is a spotty image defect on images caused by agglomerated toner liable to be caused at the time of early state of image forming after storage of the toner at a high temperature. As the popularization of color printers, the toner is becoming used and stored various environments, and a toner free from the above-mentioned problems is desired even in a severer high temperature environment than ever.
The above problems are liable to be more noticeable at a higher image forming process speed where it becomes difficult for the toner to be sufficiently charged.
In recent years, even higher image qualities than ever are demanded for images outputted from electrophotographic image forming apparatus, especially color copying machines and printers. Further, extensive popularization due to the development of network use and lower price machines thereof, the demands of such color copying machines and printers have been diversified from the professional use principally directed to a higher proportion of color images, such as (photo)graphic images to office use for which images with a lower proportion of color images are also frequently outputted. Examples of higher performances than ever required of such color copying machines and printers may include the following.
One is freeness from fog. A color image is generally formed by superposing plural colors of toner images, and if some color image is accompanied with fog, the fog is mixed with other color images to lower the resultant image quality. The difficulty of the fog is liable to be problematic especially in the office use where images of very low percentage of color image are frequently outputted in a low humidity environment.
On the other hand, in the case of formation of images with a high percentage of color image, the above-mentioned toner melt-sticking in a low temperature/low humidity environment is liable to be problematic.
Another problem is a re-transfer phenomenon. A color image is generally formed by superposition of plural colors of toner images sequentially transferred onto a transfer material, such as an intermediate transfer member and/or paper, the previous color image transferred onto such a transfer material can be transferred back to the image-bearing member at the time of transfer of a subsequent color toner image. This is the re-transfer problem. If the re-transfer problem occurs, the color of the previously transferred color is faded to result in a color change in the final image, thus causing an image quality deterioration. This problem is liable to be more noticeable at a higher image forming process speed.
Various proposals have been made so as to provide improvements to the above-mentioned problems. For example, JP-A 11-143188 has proposed a method of preventing retransfer and fog by adopting different developing conditions for plural times of color formation. JP-A 9-114126 has proposed to prevent the fog and retransfer by improvement of toner.
In spite of these proposals, however, it has been difficult to solve many of the above-mentioned problems and comply with all of high degree of requirements to high image quality in recent years.
As a further problem to be considered, there is image deterioration caused by soiling of a charging member for charging the latent image-bearing member. This is a problem of resulting in streak image irregularities in halftone images caused by obstruction of uniform charging of the latent image-bearing member due to attachment of toner particles and/or high-resistivity silica fine particles externally added to the toner.
JP-A 10-48872 has proposed a toner containing externally added inorganic fine particles having a specific average particle size and a DSC (differential scanning calorimetry) heat-absorption peak in a specific temperature range. This is effective for preventing the re-transfer problem in a process including a single transfer step, but is not sufficient to solve the other problems including the re-transfer problem encountered in process including a plurality of transfer steps and to comply with high degree of requirements in recent years.
A generic object of the present invention is to provide a toner having solved the above-mentioned problems of the prior art.
A more specific object of the present invention is to provide a toner free from toner melt-sticking onto the latent image-bearing member in a low humidity environment.
Another object of the present invention is to provide a toner free from xe2x80x9crougheningxe2x80x9d of halftone images in a low humidity environment.
Another object of the present invention is to provide a toner free from toner blot-down even after storage in a high temperature environment or during continuous image formation on a large number of sheets.
Another object of the present invention is to provide a toner free from fog even in continuous formation of images with a low percentage of color image on a large number of sheets in a low humidity environment.
Another object of the present invention is to provide a toner free from toner melt-sticking onto the latent image-bearing member even in continuous formation of images with a high percentage of color image in a low humidity environment.
A further object of the present invention is to provide a toner free from re-transfer of toner images.
A further object of the present invention is to provide a toner free from image quality lowering depending on the quality and state of the recording material.
A still further object of the present invention is to provide a process for producing such a toner, and an image forming method and an image forming apparatus using such a toner as described above.
According to the present invention, there is provided a toner, comprising: toner particles, and external additives blended with the toner particles and including (1) first inorganic fine particles having an average primary particle size of 80-800 nm of oxide of a metal selected from the group consisting of titanium, aluminum, zinc and zirconium, (2) second inorganic fine particles other than silica having an average primary particle size of below 80 nm and (3) silica fine particles having an average primary particle size of below 30 nm.
According to another aspect of the present invention, there is provided a process for producing a toner, comprising:
a first blending step of blending and dispersing toner particles containing at least a binder resin and a colorant, and first inorganic fine particles to form a toner precursor, and
a second blending step of blending and dispersing the toner precursor, and second inorganic fine particles and silica fine particles; wherein
the first inorganic fine particles have an average primary particle size of 80-800 nm and comprise an oxide of a metal selected from the group consisting of titanium, aluminum, zinc and zirconium,
the second inorganic fine particles are other than silica and have an average primary particle size of below 80 nm, and
the silica fine particles have an average primary particle size of below 30 nm.
The present invention further provides an image forming method, comprising:
(I) a step of supplying a nonmagnetic toner as described above onto a toner-carrying member from a supply roller and pressing and triboelectrically charging the nonmagnetic toner on the toner-carrying member with a toner application blade to form a charged layer of the nonmagnetic toner on the toner-carrying member,
(II) a step of developing an electrostatic latent image formed on a latent image-bearing member with the nonmagnetic toner on the toner-carrying member to form a developed toner image on the image-bearing member,
(III) a step of transferring the toner image onto a transfer material, and
(IV) a step of fixing the transferred toner image.
The present invention further provides an image forming apparatus, comprising:
(I) a plurality of image forming units each comprising:
a latent image-bearing member for bearing an electrostatic latent image thereon,
a charging device for primarily charging the image-bearing member,
an exposure means for exposing the primarily charged image-bearing member to form an electrostatic latent image thereon, and
a developing device for developing the latent image with a nonmagnetic toner as described above of a color to form a toner image of one of plural colors, and
(II) a transfer device for sequentially transferring the toner images of plural colors formed by the plurality of image forming units onto a transfer-receiving material to form superposed toner images of plural colors on the transfer-receiving material.
The present invention further provides an image forming apparatus, comprising:
(I) a latent image-bearing member for bearing an electrostatic latent image thereon,
(II) a charging device for primarily charging the image-bearing member,
(III) an exposure means for exposing the primarily charged image-bearing member to form an electrostatic latent image thereon,
(IV) a plurality of developing devices for sequentially developing the latent image with plural colors of nonmagnetic toner as described above to successively form plural colors of toner images on the image-bearing member,
(V) an intermediate transfer member for successively receiving the plural colors of toner images successively formed on and transferred from the image-bearing member to form thereon superposed toner images, and
(VI) a transfer device for simultaneously transferring the superposed toner images from the intermediate transfer member onto a transfer-receiving material.
The present invention further provides an image forming apparatus, comprising:
(I) a latent image-bearing member for bearing an electrostatic latent image thereon,
(II) a charging device for primarily charging the image-bearing member,
(III) an exposure means for exposing the primarily charged image-bearing member to form an electrostatic latent image thereon,
(IV) a plurality of developing devices for sequentially developing the latent image with plural colors of nonmagnetic toner as described above to successively form plural colors of toner images on the image-bearing member, and
(V) a transfer device for successively transferring the plural colors of toner images onto a transfer-receiving material to form superposed toner images on the transfer-receiving material.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.